title: Ultrafast energy transfer in ultrathin organic donor/acceptor blend.
abstract: It is common knowledge that poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend, a prototype system for bulk heterojunction (BHJ) solar cells, consists of a network of tens of nanometers-large donor-rich and acceptor-rich phases separated by extended finely intermixed border regions where PCBM diffuse into P3HT. Here we specifically address the photo-induced dynamics in a 10 nm thin P3HT/PCBM blend that consists of the intermixed region only. Using the multi-pass transient absorption technique (TrAMP) that enables us to perform ultra high sensitive measurements, we find that the primary process upon photoexcitation is ultrafast energy transfer from P3HT to PCBM. The expected charge separation due to hole transfer from PCBM to P3HT occurs in the 100 ps timescale. The derived picture is much different from the accepted view of ultra-fast electron transfer at the polymer/PCBM interface and provides new directions for the development of efficient devices.
authors.affiliation: dipartimento di Fisica, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
authors.forename: Ajay Ram Srimath
authors.initials: AR
authors.lastname: Kandada
authors.forename: Giulia
authors.initials: G
authors.lastname: Grancini
authors.forename: Annamaria
authors.initials: A
authors.lastname: Petrozza
authors.forename: Stefano
authors.initials: S
authors.lastname: Perissinotto
authors.forename: Daniele
authors.initials: D
authors.lastname: Fazzi
authors.forename: Sai Santosh Kumar
authors.initials: SS
authors.lastname: Raavi
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Lanzani